RE: [Xen-ia64-devel] [PATCH] [RESEND] Merge vpsr.i withevtchn_upcall_mask tosolve one trickish bug

["Tian, Kevin" <kevin.tian@xxxxxxxxx>]

Hi, Alex,
        Please help apply this one which is also the base requirement for
more coming efforts. :-)

Thanks,
Kevin
>From:Tian, Kevin
>Sent: 2006年3月30日 11:00
>Per agreement on the summit, xen/ia64 will move to event channel
>model same as xen/x86, under which event is the layer under pirq
>(external interrupt), virq, and ipi with the latter three bound
>to event ports. Within that model, no external interrupt will be
>injected directly and evtchn_upcall_mask is the flag to  control
>whether events are deliverable.
>
>So xenlinux needs to operate evtchn_upcall_mask at all places
>where it originally operates vpsr.i. However these two flags are
>presented at different shared area, and thus xenlinux can't ensure
>atomical update on two flags which leaves severe stability issues.
>One severe bug comes for this reason where some hypercall may be
>restarted infinitely when events pending.
>
>Actually based on description of future model, events become the
>superset of external interrupts and thus evtchn_upcall_mask super-
>set of vpsr.i (interrupt_delivery_enable). We can merge two flags
>into one by removing the latter. By this way, we ensure correctness
>and most importantly conform to common code which always assumes
>upon evtchn_upcall_mask.
>
>Signed-off-by Kevin Tian <kevin.tian@xxxxxxxxx>
>
>(Thanks for Isaku's comments)
>
>- Kevin

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